Chester, my mom's very first kitty developed a vaccine induced fibrosarcoma back in the late 90's when she was 9. I'll tell you about her experience but it wasn't a good one.

Mom went with the operation and it went very well but the kitty was in a lot of pain following the surgery. Unfortunately, in almost no time, the fibrosarcoma came back. The choice the vet gave mom was to amputate the leg or do another surgery. Mom crossed her fingers and did another surgery 'cause she didn't want to put the cat through an amputation. Again, the surgery went well, the kitty was in pain for a few days, but the tumour grew right back almost immediately.

Mom had no choice but to do the "as long as the quality of life is good" thing. Kitty managed for a few months but she had to be sent to the Bridge as the tumour just kept growing. Fibrosarcomas don't tend to metastasize but they are very, very aggressive.

Now, your vet hasn't given you a definitive diagnosis of fibrosarcoma if I'm reading your post correctly. Did he have the biopsied tissue examined at a lab? I'm not sure why you can't get a definitive diagnosis. I would insist on that before doing anything.

Whatever course of action you choose to take, purrs for a good outcome.